- Use "leal" for subtraction of integer constant when non-constant input to
  subtract is used more than once.
- Use "incl", "decl", and "addl" when they are smaller/cheaper than their
  leal/addl/subl equivalant.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/738073002

Cr-Commit-Position: refs/heads/master@{#25439}